Almost all fuel injectors include an injector body that defines one or more nozzle outlets, and includes a needle valve member that moves between positions to open and close the nozzle outlets. The needle valve member is typically guided within the fuel injector via a relatively tight diametrical clearance between a cylindrical guide segment of the needle valve member and a cylindrical guide bore disposed within the fuel injector body. The needle valve member includes an opening hydraulic surface that is exposed to fluid pressure in a nozzle chamber, and a spring is utilized to bias the needle valve member downward toward a closed position. In some fuel injectors, the needle valve member includes a closing hydraulic surface exposed to fluid pressure in a needle control chamber. In these instances, an electronically controlled valve is moved to fluidly connect and disconnect the needle control chamber from a low pressure passage in order to change pressures on the closing hydraulic surface of the needle valve member to facilitate movement of the needle valve member for injection events. These fuel injectors can be considered to include a direct operated check.
Over the years, engineers have continued to seek ways to inject fuel into the combustion space of a compression ignition engine in a manner that reduces the production of undesirable emissions, including but not limited to, NOx, particulate matter and unburned hydrocarbons. In general, these goals are improved by operating the fuel injector in a way that the needle valve member lifts toward an open position at a slower rate than it is moved toward a closed position. Thus, abrupt closure of the nozzle outlets is generally preferred, and a less than abrupt opening of the nozzle outlets has found favor. In this regard, many efforts have been made to improve this aspect of control including changes and refinements to electrical actuators, their associated valves, adding orifices to alter pressure change rates, changing area ratios of hydraulic features and many more considerations in a continuing effort to eek out incremental improvements in performance. Nevertheless, easily implemented improvements remain problematic and elusive.
The present disclosure is directed to one or more of the problems set forth above.